US2712602A

US2712602A - Reflection-free antenna

Info

Publication number: US2712602A
Application number: US223249A
Authority: US
Inventors: Hallen Erik Gustaf
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 1950-05-03
Filing date: 1951-04-27
Publication date: 1955-07-05
Anticipated expiration: 1972-07-05
Also published as: NL160940B; GB697193A; FR1047716A; DE849123C; NL76969C

Description

July 5, 1955 E. e. HALLEN REFLECTION-FREE ANTENNA 2 Sheets-Sheet 1 Filed April 27, 1951 N Q i m new j l 91$ m w K5. \1 r mick N a C m fi Q Q July 5, 1955 E. H L EN 2,712,602

REFLECTION-FREE ANTENNA Filed April 27, 1951 2 Sheets-Sheet 2 'lllllllllllll 27 22 Uni ML 2. Hm

United States Patent REFLECTIGN-FREE ANTENNA Erik Gustaf Halln, Stockholm, Sweden,

fonakfiebolaget L M Ericssou, company of Sweden Application April 27, 1951, Serial No. 223,249 Claims priority, application Sweden May 3, B 9 Claims. (Cl. 250-33) assignor to Tele- Stockholm, Sweden, a

tennas, for example cone-shaped or egg-shaped antennas are used, on the other hand, wider resonance peaks are obtained than when thin antennas are used, and the differenee between maximum and minimum is also relatively smaller for thick antennas. are to a certain degree broad band antennas but there remains however some variation of the conductance, and besides they are rather cumbersome.

T he object of the present invention is to achievesuch an embodiment of antennas, that the periodical variation of the admittance with the frequency quite disappears and there remains only a very feeble frequency dependence, which proceeds constantly in the same direction, whereby the antenna becomes suitable for use as broad band antenna independent of the shape of the antenna, thus also if it is a thin antenna.

The invention is based upon the following concept; The pronounced variations of. the conductance with the frequency at usual antennas are caused by the standing current wave system on the antenna with bellies and nodes, which are usually imperfect, as there is mostly only one fraction of a whole wave. As. the antenna is fed in a current belly or a current node, a great or a small conductance is obtained; Said standing wave sys tem is due to superposition of an outgoing continuous current wave and such continuous waves, asat an antenna with free end (or one free end)are reflected from the ends (or the end), or, at a frame antenna (loop antenna) have either parted in opposite directions or passed through the frame (loop) one or several times. By precluding the wave reflected at the ends (or the end) and by suppressing the meeting interferingframe wave loop wave) before it meets the first wave, it is according to the invention possible to produce a quite new current distribution on the antenna without bellies and nodes and without the strong frequency dependence of the conductance.

The essential feature of antennas (or antenna systems) according to the invention is that there is at least one antenna extending from the connection terminals, that is, in the spreading direction of the current wave with an impedanceper unit of length gradually varying in said direction for successive reduction of the. amplitude of the progressive current Wave, whereby the antenna component is arranged to prevent the development of a reflected or, more generally, an interfering current wave.

The device according to the invention has the advantage, that from the generator over the feeding line and the antenna into the air it is possible to obtain only one progressing wave without reflected or otherwise inter- Thus, these antennas ice fering waves. The same is true when the described antenna is used as receiving antenna.

The invention will be described more closely in the following with reference to the accompanying drawings.

Fig. 1a schematically shows a known transmitting antenna with two free ends and with usual current distribution, whereas Fig. 1b shows the corresponding conductance-frequency-curve.

Fig. 2a schematically shows a transmitting antenna with two free ends each having an antenna component according to an embodiment of the invention and the new current amplitude curve, whereas Fig. 2b shows the conductance-frequency-curve obtained according to the invention.

Fig. 3 shows schematically and on a larger scale a part of an antenna component according to another embodiment of the invention.

Fig. 4 schematically shows a frame antenna with an antenna component according to the invention.

Fig. 5 schematically shows a frame antenna with several feeding points and with antenna components according to the invention.

Fig. 6 shows an antenna with gradually varying resistance.

Fig. 7 shows an antenna with gradually varying resistance and inductance.

Figs. 8-10 show certain antennas with gradually varying capacitance.

In Fig. la 1 indicates the central feeding point and 2 the two cylindric antenna elements of the transmitting antenna (di-pole), and I is the total standing wave arising over the antenna, the amplitude of the wave being indicated on the ordinate. As an example it is supposed that each antenna element has a length of five half Wave lengths. It appears from Fig. lb, that the conductance and the susceptance (resistance and reactance) vary strongly with the frequency in a device according to Fig.

la. In a device according to Fig. 1a, the total standing current wave is indeed zero at the ends, but this is the case because the terminal amplitudes of each of the incoming and outgoing progressing waves extinguish each other.

Fig. 2a shows an antenna of the same type as Fig. 1a, but according to Fig. 2a each one of the antenna elements 3 is provided at its end with an antenna component 3' which in this embodiment is made of a rodshaped resistance with a resistance per unit of length gradually increasing in the direction away from the center of the antenna, that is in the spreading direction (i. e. towards the ends) of the current wave. By means of the antenna components 3 arranged according to the invention, already the amplitude I" of the outgoing current wave will-at the same frequency as in Fig. 1agradually decrease to zero at the ends (or before) in such a manner, that no reflected current wave arises and therefore no sinus-shaped standing waves are produced. It appears from Fig. 2b, that the antenna according to the invention has only a very feeble frequency dependence for the conductance, said frequency dependence always progrssing in the same direction, and a constantly very slight susceptance.

The important characteristic of the antenna components (end components) arranged according to the invention is, that they have an impedance per unit of length which gradually increases from the feeding point in the direction of the current wave up to very high values-theoretically to an infinite value, though it is sufficient with a very high finite value-owing to that they can completely outdamp the amplitude of the outgoing current. These antenna components make the antenna completely non-reflecting, and this, independent of the length and the thickness of the antenna, on the whole independent of the shape of the antenna. The antenna components according to the invention are comparatively short and will gradually weaken the amplitude of a current wave progressing on the antenna without any reflection wave arising; they may be called, using a mechanical term, (as regards the wave) electrically soft pieces. V I

It must be observed, that a resistor with a certain total resistance introduced at one or the other place would never be able, only due to its value, to prevent reflection waves completely. in order to be completely eliminating, the resistance, according to the invention, must have a varying conductivity over a certain distance, which may however be relatively short, and the transition between the antenna and ti e resistance must furthermore take place continuously'to prevent reflection from arising.

As a nears from Fi 3 the antenna com orients (end components) may according to the invention also consist of condensers arranged in series, with gradually decreasing capacitance in the direction away from the antenna terminals. in Fig. 3, 6 indicates a part of a core fixed in a suitable manner to a free antenna end for a row of cylindrical condensers arranged thereon, the exterior surfaces of which are indicated by 7" and the interior surfaces of which are indicated by 7".

Furthest to the left in Fig. 3, the exterior surfaces lie comparatively close to each other and the exterior and 1 interior surfaces over each other relatively much (great capacitance). To the right in Fig. 3 (towards the free end or" the antenna component), the distancebetween the exterior surfaces increases and the overlap decreases, becoming finally an axial distance between the exterior and the interior surfaces (small capacitance).

The antenna components may also consist of inductances (coils or parts of windings) with an inductance gradually increasing in the spreading direction of the current wave, and it is also possible to use combinations of resistance and capacitance, or resistance and inductance, or capacitance and inductance, varying per unit of length in the longitudinal direct on, or a combination of all three, always in such a manner, that the impedance per unit of length increases in the longitudinal direction.

It should be evident, that when using antennas with one or more free ends, an antenna component with gradually increasing impedance is arranged at each free end, as

illustrated in Fig. 2a and in Fig. 3.

As schematically illustrated in Fig. 4, a double-faced antenna component 1% is arranged in an antenna frame on an intermediate place in the antena, for example right opposite the feeding point ll, said antenna component having an impedance per unit of'length gradually increasing from the ends towards the center.

When using an antenna with several feeding points, for examples frame antenna 12 with two feeding points 13 according to Fig. 5, an antenna component 14 is arranged,

ing only the distance an. To increase the mechanic resistance, the resistance material should be coated with a protecting layer of for example plastic, or, if carbon paint is used, the paint be burnt.

In Fig. 7, 21 is a cylindrical base of insulating material, suitably with circular section. 'On said base a resistance material 22 is helically applied round said base with decreasing pitch and width counted from the connecting terminals 23 ofthe-antenna. Thus a successively increasing resistance in said direction is obtained due to the decreasing area, and a successively increasing inductance is obtained due to the increase of the number of revolutions per unit of length of the antenna. The desired helical shape is obtained either by directly applying the resistance material in said shape or by first covering the base and I thereafter removing material in the intervals between the with an impedance per unit of length gradually increasing 7 from the ends towards the center, at a place in the antenna betweenthe feeding points, for example half way between them.

In the preceding, the invention has been described especially with application to transmitting antennas, but it is evident, that the corresponding arguments are true also with respect to receiving antennas, whereby the connection points for the receiving line correspond to the above mentionedjfeeding points.

In Fig. 6, 111 indicates a suitably cylindrical base of insulating material, for example glass. On said base a resistance material 112 is applied with gradually decreasingthickness from the connecting terminals 113 of the antenna, which are marked by dashed lines on the draw-.

ing. This canbe obtained for example by coating a cermin number of times with a paint comprising conducting particles, for example carbon, whereby the first coating comprises the distance marked al on the drawing, the

' other coating the distance 112 and so on, and the nth coatrevolutions.

In Fig. 8, 31 is a cylindrical base of insulating materiaL.

On said base a number of plates 32 of, conducting material are arranged, the mutual distance between which gradu-- ally increases in a direction from the connecting terminals 7 gradually increases in a direction from the connecting terminals 43 of the antenna, the thickness of the plates gradually decreasing in the same direction. A quicker gradual reduction of the capacitance of the antenna is thus ob-' tained, counted from its connecting terminals.

Another modification is shown in Fig. 10. On an insulating base 51 a number of plates 52 of conducting material are arranged, the mutual distance between which gradually increases in a direction from the connecting terminals 53 0f the antenna, and the surfaces of which facing each other decrease in the same direction.

Each one of the antennasshown in Figs. 6-10 consists in its whole length of a component with gradually varying impedance per unit of length. It is naturally also possible to arrange only one part of an antenna in the described manner without departing from the scope of the invention.

It should further be observed, that the above described embodiments which are illustrated on the drawings, are only schematic examples for the illustration of the principle of the invention.

I claim:

1. In an antenna system having connection terminals at least one antenna component comprising a plurality of capacitance means in series arrangement, the capacitance of said capacitance means gradually decreasing in the direction away from said terminals of the antenna system thereby suppressing the development of a wave interfering with a current'wave generated in the antenna system.

2. An antenna system as defined in claim 1, wherein said capacitance means comprise cylindrical capacitors disposed in'axial spacing. V

s 3. An antenna system as defined in claim 2, wherein the said capacitors are mountedon an elongated insulation member mounted in alignment with one of the ends of the antenna system.

4. An. antenna system as defined in claim 1, wherein the said capacitance means comprise a plurality of electrically conductive plate members disposed perpendicu-v larly to the direction of the current wave away from said terminals and spaced one from another,-the spacings between adjacent plate members gradually increasing in the direction away from the connection terminals of the antenna system. a a

5. An antenna system as defined in claim 4, wherein the thickness of adjacent platemembers gradually decreases in the atotesaid direction.

6. An antenna system as defined in claim 1, wherein the said capacitance means comprise a plurality of electrically conductive plate members disposed perpendicularly to the direction of the current wave away from said connection terminals and spaced one from another, the thickness of adjacent plate members gradually decreasing in the direction away from the connection terminals of the antenna system.

7. An antenna system as defined in claim 1, wherein the said capacitance means comprise a plurality of electrically conductive plate members disposed perpendicuiarly to the direction of the current wave away from said connection terminals and spaced one from another, the surface areas of adjacent plate members gradually decreasing in the direction away from the connection terminals of the antenna system.

8. An antenna system as defined in claim 7, wherein the perpendicular width of adjacent plate members is gradually decreased in the aforesaid direction.

9. An antenna system as defined in claim 1, wherein the said capacitance means comprise a plurality of electrically conductive plate members disposed perpendicularly to the direction of the current Wave away from said connection terminals and spaced one from another, the

6 spacings between adjacent plate members gradually increasing in the direction away from the connection ter minals of the antenna system, the said plate members being mounted axially spaced on an elongated insulation member.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Antennas, by John D. Kraus, published by McGraw- 20 Hill, 1950, pages 214 and 215. Copy in Library.

Communication Circuits, by Ware and Reed, 2nd edition (1944), John Wiley & Sons, New York, pages 6 to 8. Copy in Scientific Library.